Mutation and propagation

DNA technology

Mutation and propagation

Genetic change can be brought about by using wild type organisms with their default DNA and inducing mutation e.g. through physiochemical routes like exposure to UV radiation or mutagenic chemicals; selective breeding to bring out recessive characteristics or emphasise particular traits; and culture of recombinant DNA that introduces artificial elements to the existing DNA, e.g. new sequences taken from a different species, an inhibitory sequence that switches off an existing function, etc.

Bacterial species can readily exchange DNA between them, as well as assimilate it from their environment. Fungi can undergo sexual reproduction to produce offspring with potentially new genotypes and phenotypes.

Culturing newly made or found mutants isn’t necessarily easy, due to their genetic instability. If introduced to a continuous culture, they may revert back to their wild type.

DNA technology

Say we are interested in the gene for insulin. Sure, we could take it straight from people, but remember humans are eukaryotes and eukaryotes have non-coding sequences within their genes called introns. The mRNA following splicing, on the other hand, has no introns! How can we make DNA from mRNA?

Take this arbitrary bit of mRNA: UCCAUGCCAUUUGGG

If we had an enzyme which could reverse the transcription back into DNA, this time intron-free, that would be great. We do – it’s called reverse transcriptase and it produces DNA. This special case of DNA is called complementary DNA – cDNA.

cDNA via reverse transcriptase: AGGTACGGTAAACCC (remember that DNA unlike mRNA is double-stranded; not shown for simplicity)

If we wanted the portion after the second G above, is there a way we could cut the DNA? It appears so. Some microorganisms have actually evolved enzymes whose job it is to invade a host and chop its DNA up at specific sequences. These enzymes are called restriction endonucleases. Each has its own..